Date: Thu, 4 Jun 2009 00:35:36 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Marcel Moolenaar <xcllnt@mac.com> Cc: kmacy@freebsd.org, marius@freebsd.org, FreeBSD Tinderbox <tinderbox@freebsd.org>, sparc64@freebsd.org, Eygene Ryabinkin <rea-fbsd@codelabs.ru>, current@freebsd.org Subject: Re: [head tinderbox] failure on sparc64/sun4v Message-ID: <alpine.BSF.2.00.0906040034350.74158@fledge.watson.org> In-Reply-To: <15550775-6B8A-414E-A579-8B518D62E06E@mac.com> References: <20090602222445.2F6017302F@freebsd-current.sentex.ca> <mqQn8SFFPOY77oNsI7n1tk5O7LE@10Ilc7MfiXA2JVIRVQpZfk7cTQ4> <rPuoszoUcXlrNmrZFDbbbNJuZzs@XX1fo6zQUfC4h0jjRC6IBz3oNH4> <alpine.BSF.2.00.0906032104100.74158@fledge.watson.org> <15550775-6B8A-414E-A579-8B518D62E06E@mac.com>
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On Wed, 3 Jun 2009, Marcel Moolenaar wrote: >> Is there a reason not just to use __aligned(64) or the like on the first >> entry of the MD PCPU structure for sun4v to avoid future MI pcpu changes >> from causing similar discomfort for the MD pcpu parts? Also, do we know >> why these alignment/sizing requirements exist for struct pcpu on sun4v but >> not other platforms? If this is about packing pcpu structures into >> properly aligned cache lines, again __aligned() might be the right approach >> to take... > > Adding __aligned(xx) doesn't make it aligned. For example, malloc(3) only > aligns at 16-byte boundaries, so any user-space structure that has > __aligned(x>16) must manually make sure that this is actually the case by > over-allocating and then adjusting the pointer to an x>16 aligned address. > Likewise for the kernel, though it's easier in the kernel to get something > that's page-aligned... FYI, I wan't sure if that was the problem that caused the alignment code in this case. However, I agree that malloc(9)'s lack of alignment support is a problem, and one that should be pretty easy to resolve by simply putting a bit of over-allocation code in malloc(9), and adding a malloc_aligned(9) variation, or perhaps just an M_CACHEALIGN flag. Robert N M Watson Computer Laboratory University of Cambridge
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